Investment in Securities (Proceeds, Realized Gains (Losses) on Sales) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Securities, Available-for-sale [Line Items]
Proceeds	$ 494,704,000	$ 204,629,000	$ 787,652,000	$ 1,723,038,000
Available-for-sale Securities, Gross Realized Gains	8,464,000	5,968,000	16,511,000	25,152,000
Available-for-sale Securities, Gross Realized Losses	(10,416,000)	(6,616,000)	(11,997,000)	(10,416,000)
Available-for-sale Securities, Gross Realized Gain (Loss)	(1,952,000)	(648,000)	4,514,000	14,736,000
Available-for-sale securities Realizes Losses - adjustments to cost basis of certain securities	(82,000)	(13,800,000)	(1,300,000)	(13,800,000)
Agency RMBS
Securities, Available-for-sale [Line Items]
Proceeds	417,359,000	140,109,000	492,218,000	1,425,590,000
Available-for-sale Securities, Gross Realized Gains	2,997,000	4,673,000	3,378,000	13,698,000
Available-for-sale Securities, Gross Realized Losses	(6,930,000)	(614,000)	(7,291,000)	(3,231,000)
Available-for-sale Securities, Gross Realized Gain (Loss)	(3,933,000)	4,059,000	(3,913,000)	10,467,000
Non-Agency RMBS and CMBS
Securities, Available-for-sale [Line Items]
Proceeds	18,544,000	20,621,000	141,752,000	98,423,000
Available-for-sale Securities, Gross Realized Gains	2,900,000	1,031,000	9,139,000	9,432,000
Available-for-sale Securities, Gross Realized Losses	(152,000)	(2,769,000)	(1,147,000)	(3,729,000)
Available-for-sale Securities, Gross Realized Gain (Loss)	2,748,000	(1,738,000)	7,992,000	5,703,000
CLOs
Securities, Available-for-sale [Line Items]
Proceeds	43,426,000	7,172,000	129,001,000	41,714,000
Available-for-sale Securities, Gross Realized Gains	2,320,000	0	3,491,000	1,122,000
Available-for-sale Securities, Gross Realized Losses	(3,250,000)	(3,178,000)	(3,429,000)	(3,202,000)
Available-for-sale Securities, Gross Realized Gain (Loss)	(930,000)	(3,178,000)	62,000	(2,080,000)
Other Securities
Securities, Available-for-sale [Line Items]
Proceeds	15,375,000	36,727,000	24,681,000	157,311,000
Available-for-sale Securities, Gross Realized Gains	247,000	264,000	503,000	900,000
Available-for-sale Securities, Gross Realized Losses	(84,000)	(55,000)	(130,000)	(254,000)
Available-for-sale Securities, Gross Realized Gain (Loss)	$ 163,000	$ 209,000	$ 373,000	$ 646,000